Veteran French politician Dominique Baudis has challenged judges to investigate allegations that he was involved in sado-masochistic orgies organised by a convicted serial killer.

Mr Baudis, who heads France's media watchdog the CSA, strongly denies the accusations and says he is facing a political vendetta.

His challenge follows reports that the convicted killer, Patrice Alegre, has accused Mr Baudis of being involved in the orgies.

Two prostitutes have already made the same allegation.

Alegre, who appeared before magistrates at the weekend, also confessed to the murder of two more people - a female prostitute and a transvestite - in addition to the five he is known to have killed.

He said he carried out the murders under instructions from public figures, who feared the transvestite would release pictures taken with a hidden camera and that the prostitute "would not keep her mouth shut".

The orgies are alleged to have taken place in Toulouse, when Mr Baudis was mayor of the city.

One city official, chief prosecutor Jean Volff, resigned over the scandal last week.

Mr Volff said he had been named in the prostitutes' testimony to police but described their story as "totally implausible".

'Revenge'

Mr Baudis, an influential figure in the governing centre-right party, UMP, has led a vocal campaign to ban hardcore pornography from television over the last year.

The former mayor says he believes that elements of the pornography industry may be spreading the orgy stories in order to get revenge on him for the campaign.

He has asked to be put under investigation so that his lawyer can gain access to the evidence against him.

"It is unacceptable that a man's honour can be tainted by the words of a murderer serving a life sentence and of two prostitutes," Mr Baudis' lawyer, Francis Szpiner, told Liberation newspaper.

Asked why his client had taken the unusual step of asking to be placed under judicial investigation, Mr Szpiner said it was "the only way to fight on equal terms against the purveyors of slander".

Being placed under formal investigation is a step that falls short of criminal charges but implies a prima facie case.

Cocaine

Alegre, for his part, said he wanted the truth to be told.

"I cannot accept that the truth will be suppressed because the people involved are people in power," he wrote in a letter sent secretly from prison and published in Monday's French press.

"[The two prostitutes] are telling the truth when they say they went with me to sado-masochistic parties... and that certain members of the Toulouse bourgeoisie were there, and everyone was going for the cocaine," Alegre wrote.

Alegre was jailed for life in 2002 for six rapes and five murders.

He is also under investigation in connection with a criminal network in Toulouse said to have involved minors and cocaine.